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Violating consensual reality
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Discussion Starter #1
My shop manual does not list the duration of my stock cam so I am trying to figure out what I have.

It says:
Intake Valve Opens BTC 34*
Closes ABC 86*

Exhaust Valve Opens BBC 68*
Closes ATC 52*

This is the calculator I used
http://www.wallaceracing.com/camcalc.php
It says:
Your cam has an Overlap of 86.00 degrees and has in Intake Duration of 300.00 degrees.
The Exhaust Duration is 300.00 degrees.
The Inlet Cam has an Installed Centerline of 116.00 degrees ATDC.
The exhaust cam has an Installed Centerline of 98.00 degrees BTDC.

As a reality check, can anyone tell me if this is correct? Thanks.

Strummin
 

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Save a horse, Ride a Cowboy.
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strummin67 said:
My shop manual does not list the duration of my stock cam so I am trying to figure out what I have.

It says:
Intake Valve Opens BTC 34*
Closes ABC 86*

Exhaust Valve Opens BBC 68*
Closes ATC 52*

This is the calculator I used
http://www.wallaceracing.com/camcalc.php
It says:
Your cam has an Overlap of 86.00 degrees and has in Intake Duration of 300.00 degrees.
The Exhaust Duration is 300.00 degrees.
The Inlet Cam has an Installed Centerline of 116.00 degrees ATDC.
The exhaust cam has an Installed Centerline of 98.00 degrees BTDC.

As a reality check, can anyone tell me if this is correct? Thanks.

Strummin
Those are not specs for .050, but "seat duration" or maybe .006 lift as some companies use.

When LSA is determined, installing straight-up is when the Lobe Separation Angle = Installed Intake CenterLine.

I conclude that your information says that the LSA is 116 and therefore straight-up if timed 116 ATDC.

But yes, they are correct. Determining .050 specs is impossible with the information you provide.
 

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The trick is to know at what tappet lift the specs are given. I suspect that a stock cam with the figures you are given would be a zero tappet lift. Problem with this is that no aftermarket cam will be measured at zero, so there is no way to compare your stock cam to any other cam. Aftermarket grinders usually list two figures, with the tappet at 0.006" lift and at 0.050" lift. 0.050" is the most realistic figure to compare cams, as it eliminates some of the opening and closing ramps which can be very different among different cams.

What I have done in the past when confronted with this question is to measure the cam myself. You'll need the block, crank, cam and timing gears installed. If you have a lathe, turn out a steel bar equal to or a little less than the diameter of the lifters used in the motor. Make the length long enough so that the bar is just above the block deck when installed in the lifter bore on the cam lobe. With the block on an engine stand, rotate it so that the deck is up so that gravity will keep the bar riding on the cam lobe. Install a degree wheel on the crank and make sure which lobe you are measuring, intake or exhaust. Check the cylinder head for intake/exhaust valve placement if you are unsure. Use a magnetic dial indicator with a 1" travel and mount it to the deck with the indicator probe parallel with the bar looking at it from the front and from the side. Preload the probe by about 0.100" with the bar on the heel of the cam lobe. Zero the dial. Rotate the crank to where the cam moves the needle just slightly. Mark that spot on the degree wheel. Continue rotating the crank until you show 0.050" lift on the dial. This will be your zero point at which you will begin measuring the duration. Continue rotating the crank until the bar is down on the heel of the cam again and the dial has stopped moving. Back up 0.050" and that will be the closing point at 0.050" tappet lift. Count the number of degrees on the wheel between these points and you have the 0.050" tappet lift duration of that lobe. To measure the cam lift, just rotate the crank until the bar is on the heel of the lobe. Zero the dial and rotate the crank through 2 complete revolutions, noting the highest lift on the dial. Multiply the lift noted on the dial by the rocker arm ratio for the motor and you have theoretical valve lift (theoretical because lash has not been taken into consideration).

If there is a simpler way, I'm sure one of the other members will step in and explain it. I'm old and set in my ways, so this is how I have always done it.

If you will make one of these bars for each motor you will be working on, you'll prize them as valuable additions to your toolbox. If you don't have a lathe, any local machine shop can make these for you for cheap. Give the machinist the tappet bore and allow him a tolerance of plus 0.000", minus 0.002".
 

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techinspector1 said:
The trick is to know at what tappet lift the specs are given. I suspect that a stock cam with the figures you are given would be a zero tappet lift. Problem with this is that no aftermarket cam will be measured at zero, so there is no way to compare your stock cam to any other cam. Aftermarket grinders usually list two figures, with the tappet at 0.006" lift and at 0.050" lift. 0.050" is the most realistic figure to compare cams, as it eliminates some of the opening and closing ramps which can be very different among different cams.

What I have done in the past when confronted with this question is to measure the cam myself. You'll need the block, crank, cam and timing gears installed. If you have a lathe, turn out a steel bar equal to or a little less than the diameter of the lifters used in the motor. Make the length long enough so that the bar is just above the block deck when installed in the lifter bore on the cam lobe. With the block on an engine stand, rotate it so that the deck is up so that gravity will keep the bar riding on the cam lobe. Install a degree wheel on the crank and make sure which lobe you are measuring, intake or exhaust. Check the cylinder head for intake/exhaust valve placement if you are unsure. Use a magnetic dial indicator with a 1" travel and mount it to the deck with the indicator probe parallel with the bar looking at it from the front and from the side. Preload the probe by about 0.100" with the bar on the heel of the cam lobe. Zero the dial. Rotate the crank to where the cam moves the needle just slightly. Mark that spot on the degree wheel. Continue rotating the crank until you show 0.050" lift on the dial. This will be your zero point at which you will begin measuring the duration. Continue rotating the crank until the bar is down on the heel of the cam again and the dial has stopped moving. Back up 0.050" and that will be the closing point at 0.050" tappet lift. Count the number of degrees on the wheel between these points and you have the 0.050" tappet lift duration of that lobe. To measure the cam lift, just rotate the crank until the bar is on the heel of the lobe. Zero the dial and rotate the crank through 2 complete revolutions, noting the highest lift on the dial. Multiply the lift noted on the dial by the rocker arm ratio for the motor and you have theoretical valve lift (theoretical because lash has not been taken into consideration).

If there is a simpler way, I'm sure one of the other members will step in and explain it. I'm old and set in my ways, so this is how I have always done it.

If you will make one of these bars for each motor you will be working on, you'll prize them as valuable additions to your toolbox. If you don't have a lathe, any local machine shop can make these for you for cheap. Give the machinist the tappet bore and allow him a tolerance of plus 0.000", minus 0.002".

I pretty much use this same method.
I have two such bars that I made up. One is made from .875 round stock and is turned down to .842 for half it's length. I use one end for Chevy's or I turn it over to do Fords. The other is made for Mopar and AMC's. They're both made from D-2 and hardened which isn't needed but I was ambitious that day.
 

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Posted by engineczar:
"I use one end for Chevy's or I turn it over to do Fords."

Perfect. I never thought of using one bar for two applications. :spank:
 

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Strummin, on the NAPA site you do have to click on the part# and price shown to see all the cam specs.....everything listed from durations to lsa's to open/close *'s for intake and exhaust

I shouldn't have listed Autozone....

Advance Auto does list the spec's with the price but doesn't give nearly as much detail as the NAPA site

what is the car/yr/motor/ etc....
 

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Violating consensual reality
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Discussion Starter #12
Red.
I found the area you were talking about. Those specs if not dead on are close enough. Thanks.

Strummin
 

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Hey, that NAPA tip was a good one. Here's the skinny on the 194 stock cam....

Advertised Duration (Exhaust):270 Deg
Advertised Duration (Intake):260 Deg
Cam Lift (Exhaust):.280"
Cam Lift (Intake):.265"
Cam Timing at .050" Lobe Lift (Exhaust Close):13 Deg BTC
Cam Timing at .050" Lobe Lift (Exhaust Open):37 Deg BBC
Cam Timing at .050" Lobe Lift (Intake Close):22 Deg ABC
Cam Timing at .050" Lobe Lift (Intake Open):8 Deg ATC
Degrees Overlap:45 Deg
Duration at .050" Lobe Lift (Exhaust):204 Deg
Duration at .050" Lobe Lift (Intake):194 Deg
Lobe Centerline (Exhaust):115 Deg
Lobe Centerline (Intake):105 Deg
Valve Lash (Exhaust):Hyd.
Valve Lash (Intake):Hyd.
Valve Lift (Exhaust):.490"
Valve Lift (Intake):.464"

Adding the intake and exhaust centerlines together and dividing by two gives a lobe seperation angle of 110*. The advertised duration was probably figured at a tappet lift of 0.006".
 

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Violating consensual reality
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Discussion Starter #15
I think this is closer to what I have:

Advertised Duration (Exhaust):244 Deg
Advertised Duration (Intake):244 Deg
Cam Lift (Exhaust):.222"
Cam Lift (Intake):.222"
Cam Timing at .050" Lobe Lift (Exhaust Close):19 Deg After Top Center
Cam Timing at .050" Lobe Lift (Exhaust Open):11 Deg Before Bottom Center
Cam Timing at .050" Lobe Lift (Intake Close):12 Deg After Bottom Center
Cam Timing at .050" Lobe Lift (Intake Open):20 Deg After Top Center
Degrees Overlap:33 Deg
Duration at .050" Lobe Lift (Exhaust):172 Deg
Duration at .050" Lobe Lift (Intake):172 Deg
Lobe Centerline (Exhaust):104 Deg
Lobe Centerline (Intake):106 Deg
Valve Lash (Exhaust):Hydraulic
Valve Lash (Intake):Hydraulic
Valve Lift (Exhaust):.389"
Valve Lift (Intake):.389"

I did find the specs you posted but it's one of the two High Performance cams they have.

Strummin
 
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